linux-kernel - Re: [PATCH v2] mm/mmap.c: refine find_vma_prev with rb

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Message-ID: <20190809083122.GA32128@richard>
Date:   Fri, 9 Aug 2019 16:31:22 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        akpm@...ux-foundation.org, mhocko@...e.com,
        kirill.shutemov@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/mmap.c: refine find_vma_prev with rb_last

On Fri, Aug 09, 2019 at 10:03:20AM +0200, Vlastimil Babka wrote:
>On 8/9/19 2:19 AM, Wei Yang wrote:
>> When addr is out of the range of the whole rb_tree, pprev will points to
>> the right-most node. rb_tree facility already provides a helper
>> function, rb_last, to do this task. We can leverage this instead of
>> re-implement it.
>> 
>> This patch refines find_vma_prev with rb_last to make it a little nicer
>> to read.
>> 
>> Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
>
>Acked-by: Vlastimil Babka <vbabka@...e.cz>
>
>Nit below:
>
>> ---
>> v2: leverage rb_last
>> ---
>>  mm/mmap.c | 9 +++------
>>  1 file changed, 3 insertions(+), 6 deletions(-)
>> 
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 7e8c3e8ae75f..f7ed0afb994c 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -2270,12 +2270,9 @@ find_vma_prev(struct mm_struct *mm, unsigned long addr,
>>  	if (vma) {
>>  		*pprev = vma->vm_prev;
>>  	} else {
>> -		struct rb_node *rb_node = mm->mm_rb.rb_node;
>> -		*pprev = NULL;
>> -		while (rb_node) {
>> -			*pprev = rb_entry(rb_node, struct vm_area_struct, vm_rb);
>> -			rb_node = rb_node->rb_right;
>> -		}
>> +		struct rb_node *rb_node = rb_last(&mm->mm_rb);
>> +		*pprev = !rb_node ? NULL :
>> +			 rb_entry(rb_node, struct vm_area_struct, vm_rb);
>
>It's perhaps more common to write it like:
>*pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;
>

Do you prefer me to send v3 with this updated?

>>  	}
>>  	return vma;
>>  }
>> 

-- 
Wei Yang
Help you, Help me